With the recent development in color image output technology such as the technology to display or output a color image, various documents or data such as a webpage created by an individual or a corporation are generated with characters or graphical images of many different colors. In one example, the characters may be displayed in color in order to notify a viewer of the document of the importance of information conveyed by the characters displayed in color. In another example, the data illustrated in a graph may be displayed in different colors in order to notify a viewer of the document that these data belong to different groups. In order to accurately interpret the information included in such document produced in color, the viewer is expected to accurately recognize the differences in color as well as the characters and the images.
For example, if the viewer happens to be a person with color vision defects who sees the color differently from ordinary people, the viewer may not correctly recognize information conveyed by the color. For example, if the person has difficulty in detecting the red color and the green color, the person may only recognize information in the blue color if the graph provides information in red, green, and blue colors.
According to the recent physiological and medical research related to the human vision, various color vision defect types are known including the red-green color blindness, the yellow-blue color blindness, and the total color blindness. According to the Color Universal Design Organization (CUDO), the human vision types can be classified into various types including the Common type (C-type), the Protanopia type (P-type) such as the strong Protanopia and the weak Protanopia, Deuteranopia type (D-type) such as the strong Deuteranopia type and the weak Deuteranopia type, Tritanopia type (T-type), and Achromatopia type (A-type). The person with the C-type vision is the person with the ordinary color vision, while the person with the other type vision is the person with the color vision defects.
In order to accurately convey information to those who may have the color vision defects, the original colors of the information may be converted to the colors that can be easily recognized by a person with the color vision defects when a request is received from the person with the color vision defects, for example, as described in the Japanese Patent Application Publication Nos. 2002-248096, 2000-181426, and 2006-246072.